(a) Field of the Invention
The present invention relates to a data transmission system having a plurality of dynamic route control units and, more particularly, to a data transmission system for transmitting data packets to and from a plurality of other transmission systems through a network by using a dynamic route control technique.
(b) Description of the Related Art
A dynamic route control technique for a conventional data transmission system is described in IETF (Internet Engineering Task Force), RFC (Request For Comments) 2328, “OSPF (Open Shortest Path First) Version2”, August, 1998 by John Moy. The described dynamic route control technique uses a single route control protocol, or single route control unit, in a single route control domain.
FIG. 1 shows the data transmission system (DTS) using the dynamic route control technique described in the above publication. The data transmission system 10 includes a dynamic route control unit 20, a routing table 60 and a plurality (n) of interfaces 91, wherein the data transmission system 10 is connected to other data transmission systems 71 under the control by interfaces 91.
The dynamic route control unit 20 performs transmission of route control data with respect to all the interfaces 91 provided in the data transmission system 10. The dynamic route control unit 20 also performs calculation for all the routes in the network between these interfaces 91 and other data transmission systems 71 that are accessible from the interfaces 91 through the network. The term “route control data” as used herein means the information with respect to the interfaces in the data transmission system 10, the information including addresses, communication costs etc., of the other data transmission systems that are accessible via the interfaces 91.
Adjacent two of the data transmission systems 71 and 10 in the network performs transmission of the route control data therebetween by using the route control processing. In other words, the data transmission systems 10 and 71 in the domain share the route control data among them, which are created by all the data transmission systems 10 and 71 in the domain. Thus, it may happen that the data transmission system 10 having a plurality of interfaces 91 receives the same route control data from a plurality of other data transmission systems 71. In such a case, the data transmission system 10 compares the route control data thus received against the route control data stored in the database of the data transmission system 10. If both the route control data are the same, the route control data thus received is discarded for avoiding a duplication. The term “domain” as used herein means an area of network dynamically route-controlled.
The data transmission system 10 creates the graph of the network configuration including the other data transmission systems 71 in the domain based on the route control data stored therein, and also calculates to obtain the minimum distance route between the own system and each of the other data transmission systems in the network configuration. In short, the dynamic route control unit 20 performs both transmission of the route control data and calculation for the minimum distance route in the conventional data transmission system 10.
In the conventional data transmission system 10, the single dynamic route control unit 20 performing both transmission of the route control data and calculation for the minimum distance route may be unable to perform both the tasks due to overload thereof if the number of the interfaces 91 provided in the entire domain is larger compared to the ability thereof. Or else, even if the dynamic route control unit 20 is somehow able to perform both the tasks, the larger time length for the tasks may cause a larger time length needed to stabilize the data route in the case of change in the network configuration.
More specifically, a large number of interfaces 91 associated with the data transmission system 10 increases the number of times for transmission of the route control data, and also increases the burden of the calculation for the data route on the dynamic route control unit 20. In worst case, the transmission processing itself may exceed the capability of the dynamic route control unit 20, whereby the dynamic route control unit 20 is unable to perform the data transmission itself by using the associated interfaces 91. This limits the possibility of extension of the number of interfaces in the network.